The present disclosure relates generally to a mobile device with multiple communication capabilities, and more specifically, to an interface unit of the mobile device. Mobile devices may provide multiple communication capabilities including communication between the mobile device and an auxiliary device coupled to the mobile device. A headphone output (e.g., 3.5 mm jack, USB) on the mobile device may be configured to send and/or receive analog and digital data with auxiliary devices such as acoustic, optical and electromagnetic devices (e.g. FM radio transmitter, credit card readers, audio and video signals, etc.). In some cases, the presence of an audio signal may create interference (e.g., noise) on other communications over the headphone interface. One cause of the interference may be the use of a shared ground.